The paper presents a practical approach to assessing the risks of exposure to the infective agents from transmissible spongiform encephalopathies. Current data on the infectivity of bovine tissues have been reviewed and values for use in risk assessment studies proposed for the infectivity of central nervous system and other tissues, the development of infectivity through the incubation period and the cattle-human species barrier. A study to assess the risk of exposure to BSE infectivity in cattle disposed of during the 2001 foot and mouth epidemic in the UK by burning in pyres or burial is used to illustrate the application of TSE risk assessment and the way in which it can be used as an input to decision making.